David Young
Maneuver Analysis
1. Maneuver – Power-Off Stalls.
2. Description – A sudden loss in lift and increase in drag due to exceeding the critical
angle of attack in the approach-to-landing configuration.
3. Objective – To familiarize the student with situations that may produce a power-off stall,
and to teach the student how to recognize and recover should one be accidentally
encountered.
4. Contents –
a. An understanding of the aerodynamics of normal and slow flight.
b. An understanding of coordinated flight.
c. An understanding of the aerodynamics of a stall.
d. The ability to recognize an imminent power-off stall.
e. The ability to recover from a power-off stall.
5. Analysis –
a. A stall occurs when the airflow over the airfoils is disrupted, and a sudden loss of
lift occurs.
i. This occurs when the angle of attack exceeds what is called the critical
angle of attack.
1. Chord Line – The imaginary line drawn from the leading edge to
the trailing edge of an airfoil (refer to Figure A).
2. Relative Wind – The direction of the airflow with respect to an
airfoil. In simple terms, it’s the rush of “wind” you feel when you
stick your hand out the car window. It is formed by motion
through the air (refer to Figure A).
3. Angle of Attack – The angle formed between the chord line and the
relative wind.
4. Critical Angle of Attack – The angle of attack at which the aircraft
stalls regardless of airspeed, flight attitude, or weight.
b. In straight and level cruise flight, the air does not separate when it flows over the
wing (refer to upper left image of Figure B).
c. As the angle of attack increases, the air begins to separate near the trailing edge,
but not enough to disrupt the entire airflow over the wing (refer to upper middle
image of Figure B).
d. As the angle of attack reaches the critical angle of attack, the air separates closer
and closer to the leading edge. Eventually, the air is turbulent enough to disrupt
the airflow over the upper curve of the wing, and lift is lost due to the sudden
increase in pressure over the top of the wing (refer to upper right image of Figure
B).
Young 2, XI-C
e. When performing a stall, the inner portion of the wing (called the wing root) has a
relatively low angle of incidence.
i. Angle of Incidence – The angle formed between the chord line of the wing
and the longitudinal axis of the aircraft.
ii. Because the wing root has a higher angle of incidence, it has a higher
angle of attack than the wing tips.
1. This ensures that the ailerons, which are on the outer portion of the
wing, are the last control surface to be stalled when a stall occurs.
This helps maintain control during a stall.
f. Note that an aircraft can stall at ANY airspeed, power setting, and attitude.
i. Things like landing gear and flaps can change the stall SPEED, but the
critical angle of attack will remain constant unless the camber, or shape, of
the wing is changed (i.e. flaps).
ii. Center of gravity (the point at which the plane would balance if held up at
that point) can affect the stall speed.
1. As the CG moves aft, the aircraft flies at a lower angle of attack for
a given airspeed. Therefore, the critical angle of attack will be
exceeded at a lower airspeed.
a. An excessively aft CG may cause a tendency to pitch up
during the stall recovery, which will make recovery
especially difficult.
2. As the CG moves forward, the aircraft flies at a higher angle of
attack for a given airspeed. Therefore, the critical angle of attack
will be exceeded at a higher airspeed.
iii. Load Factor, or the ratio of the lifting force produced by the wings to the
weight of the aircraft, can negatively affect stall speed. This is the “G
Force” (refer to Figure C).
1. Stall speed increases in proportion to the square root of the load
factor.
a. For example, if the stall speed is 50 kts, the aircraft will
stall at 100 kts with a load factor of 4 Gs.
2. Note that load factor’s effect on stall speed is very apparent during
turns, during which the stall speed increases due to the increased
load factor.
iv. Any sort of ice on the wings will disrupt the smooth airflow over the
wings, and, therefore, increase drag and reduce lift. This results in a lower
stall speed.
v. Turbulence can suddenly shift the relative wind, which may cause the
angle of attack to exceed the critical angle of attack, and, therefore, stall.
Young 3, XI-C
g.
h.
i.
j.
k.
l.
m.
n.
1. It is important to fly at a higher-than-normal approach speed
during approach-to-landing in order to reduce the likelihood of
exceeding the critical angle of attack due to turbulence.
2. Turbulence can also cause an excessive load factor on the aircraft,
which will increase the stall speed.
Common scenarios that a power-off stall may be encountered include:
i. Attempting to recover from a high sink rate by only pitching up.
ii. Improper airspeed control on final approach.
iii. Attempting to stretch a glide.
To actually enter a power-off stall, begin by performing two clearing turns.
i. Note that you must be at an altitude from which you can safely recover
from a stall. The minimum is 1,500 ft AGL.
Perform a GUMPP check.
i. G – Gas (check that the fuel selector is on the fuller tank).
ii. U – Undercarriage (verify that the gear is down when below Vle).
iii. M – Mixture (Full rich, or leaned if above 5,000 ft MSL).
iv. P – Propeller (Full prop if equipped with a constant speed prop).
v. P – Pump (Turn the electric fuel pump ON if so equipped).
Begin slow flight and configure the aircraft for landing.
When slowed down to approach speed, pitch down to obtain about a 500 fpm
descent while maintaining approach speed.
i. Maintain heading with minor corrections.
When established in a descent, simultaneously reduce the throttle to idle while
pitching the nose up to slightly above the horizon. Hold the nose there as the
airspeed bleeds off. The controls will begin to feel very mushy because of their
reduced effectiveness (due to reduced airflow over the control surfaces).
i. If asked to perform the maneuver in a turn, simply use a shallow climbing
turn. Just be sure to keep the aircraft coordinated at all times.
The stall horn should begin blaring, which means you are between 5 and 10 knots
above stall speed.
i. Announce to the instructor “stall horn.”
ii. As with all phases of flight, it is very important to keep the aircraft
coordinated. An uncoordinated, stalled aircraft may enter a spin, which is
more difficult to recover from.
iii. If one wing begins to rise, step on the high wing. Do NOT use ailerons
because they may cause the aircraft to enter a spin.
Next, the plane will begin to buffet. The aircraft may seem to shake.
i. This is due to the disrupted airflow over the control surfaces.
ii. Announce to the instructor “buffet.”
iii. Note that things might get suddenly much quieter than normal.
Young 4, XI-C
o. When the stall actually occurs, the nose will suddenly drop.
i. Simultaneously pitch down enough to get air flowing back over the wings
(about 5º - 10º pitch down) while applying full prop and power.
1. If the aircraft begins to buffet again, release some elevator
backpressure to keep from stalling again.
2. The goal is to lose as little altitude as possible. Pitch down enough
to restore enough lift, but not so much that excessive altitude is
lost. This will put the nose about 3 inches below the horizon.
ii. Roll wings level.
iii. Use right rudder to counteract the left turning tendencies and to stay
coordinated.
iv. Immediately release one notch of flaps.
v. When at Vso + 10 kts, begin pitching up to begin a climb out (if in real life,
otherwise maintain altitude). Be sure to use smooth pressures to prevent a
load factor-induced stall.
vi. When the VSI indicates a positive climb rate, take off the next notch of
flaps and bring the landing gear up. Pitch for Vx.
vii. When established at Vx, take the last notch of flaps off.
viii. Climb to a safe altitude, or an altitude that is specified by your instructor.
6. Visual Cues –
a. Use the engine cowling and the horizon to determine the level flight pitch attitude.
b. As airspeed decreases, the horizon will move further and further down the
cowling.
c. When pitching up from the descent to enter the stall, the nose should not be too
far above the horizon.
d. The horizon will suddenly move up on the cowling when the aircraft stalls.
7. Instrument Cues –
a. Use the attitude indicator to determine level flight.
b. The directional gyro will tell you if you have strayed off course.
c. The ball will swing to the right side of the inclinometer during the recovery from
the stall.
8. PTS Standards –
a. Private Pilot –
i. Exhibits knowledge of the elements related to power-off stalls.
ii. Selects an entry altitude that allows the task to be completed no lower than
1,500 feet (460 meters) AGL.
iii. Establishes a stabilized descent in the approach or landing configuration,
as specified by the examiner.
iv. Transitions smoothly from the approach or landing attitude to a pitch
attitude that will induce a stall.
Young 5, XI-C
v. Maintains a specified heading, ±10°, in straight flight; maintains a
specified angle of bank not to exceed 20°, ±10°; in turning flight, while
inducing the stall.
vi. Recognizes and recovers promptly after the stall occurs by simultaneously
reducing the angle of attack, increasing power to maximum allowable, and
leveling the wings to return to a straight-and-level flight attitude with a
minimum loss of altitude appropriate for the airplane.
vii. Retracts the flaps to the recommended setting; retracts the landing gear, if
retractable, after a positive rate of climb is established.
viii. Accelerates to Vx or Vy speed before the final flap retraction; returns to the
altitude, heading, and airspeed specified by the examiner.
b. Commercial Pilot –
i. Exhibits knowledge of the elements related to power-off stalls.
ii. Selects an entry altitude that allows the task to be completed no lower than
1,500 feet (460 meters) AGL.
iii. Establishes a stabilized descent in the approach or landing configuration,
as specified by the examiner.
iv. Transitions smoothly from the approach or landing attitude to a pitch
attitude that will induce a stall.
v. Maintains a specified heading, ±10° in straight flight; maintains a
specified angle of bank, not to exceed 20°, ±5°, in turning flight while
inducing the stall.
vi. Recognizes and recovers promptly as the stall occurs by simultaneously
reducing the angle of attack, increasing power to maximum allowable, and
leveling the wings to return to a straight-and-level flight attitude with a
minimum loss of altitude appropriate for the airplane.
vii. Retracts the flaps to the recommended setting, retracts the landing gear if
retractable after a positive rate of climb is established.
viii. Accelerates to Vx or Vy speed before the final flap retraction; returns to the
altitude, heading, and airspeed specified by the examiner.
9. Common Errors –
a. Failure to establish the aircraft configuration before entering the stall.
b. Improper pitch, heading, and bank control during the stalls.
c. Rough or uncoordinated flight.
d. Failure to recognize the imminent stall.
e. Failure to stall.
f. Delayed stall recovery.
g. Excessive loss of altitude.
h. Entering a secondary stall during the recovery.
10. References –
a. AFH, Ch. 5
b. Gleim’s Flight Instructor Flight Maneuvers, Part II, Unit XI
c. FAA-S-8081-12B
d. FAA-S-8081-14A
Young 6, XI-C
Figure A
Figure B
Young 7, XI-C
Figure C